This invention relates to friction snubbed railway trucks and, in particular, to both lateral and vertical damping of what is commonly known as a three piece truck.
Geometrical constraints of past friction snubbed railway track designs of either constant or variable damping have limited the amount of damping. These geometrical constraints have further limited the amount of truck squaring moment between the main elements of the three piece truck.
Recent three piece truck designs using longer travel springs have aggravated an ever-existing wear problem between the main elements of the three piece truck. This sustained wear problem is caused by light car truck hunting, lack of lateral damping capability at loaded car, loaded car rocking, loaded car pitching and bouncing, or various combinations of these conditions.
The friction snubbing means of a conventional three piece truck is designed primarily to dampen the periodic oscillations of the truck bolster as it vibrates both vertically and horizontally on its supporting springs in respect to the two side frames during normal operation. The limit cycle of the vertical oscillations is the solid spring condition of the bolster support springs. This condition is not uncommon in underdamped trucks. The limit cycle of the lateral oscillations of the truck bolster is the contacting of the bolster gibs with the side frame columns. This condition appears normally at the contact of the bolster inner gibs with the inside surfaces of the side frame columns. Truck hunting and excessive vertical car bouncing promote rapid wear of the relatively soft cast steel parts at this element interface.
In addition, known three piece truck designs utilize snubbing structures that possess lesser dimensions in the horizontal direction than in the vertical direction. These narrower dimensions of past snubbing means do not give adequate squaring moment capabilities, an adverse problem especially apparent on variable damped trucks.
Due to geometrical constraints previously mentioned, some past designs of constant damped trucks do not have the elements of the damping mechanism in full friction face contact at all positions of bolster travel. Thus, the unit pressure between the friction elements is variable and at some conditions of bolster travel, the resulting higher unit pressure promotes more rapid wear of the friction elements.